Negative
Frequency-Dependent Selection
An orchid species occurs in two
color forms (morphs), red and blue. Neither morph
provides any nectar to the pollinator: pollinator insect
species quickly learn to avoid the more
common morph, but have less opportunity to learn about the
less common morph. Therefore, either morph has lower fitness
when common (e.g., Wblue 
2
as f(blue) 1
and Wred 1
as f(red)
1) [top]. [Bottom] Minimal population
fitness occurs when both morphs are at intermediate
frequency. This equilibrium is unstable:
deviation to either side will lead to fixation of one morph
or the other. Negative frequency-dependent selection de-stabilizes
population polymorphism. Compare dynamics with
positive selection in S&R2019
Fig 4.12.
2
as f(blue) 1
and Wred 1
as f(red)
1) [top]. [Bottom] Minimal population
fitness occurs when both morphs are at intermediate
frequency. This equilibrium is unstable:
deviation to either side will lead to fixation of one morph
or the other. Negative frequency-dependent selection de-stabilizes
population polymorphism. Compare dynamics with
positive selection in S&R2019
Fig 4.12.[note to self: curves are backwards, swap 4.11
& 4.12 ?]